Throughout the business world, inkjet printing systems are extensively used for image reproduction. Inkjet printing systems frequently make use of an inkjet printhead mounted within a carriage that is moved back and forth across print media, such as paper. As the printhead is moved across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text. Such systems may be used in a wide variety of applications, including computer printers, plotters, copiers and facsimile machines.
Ink is provided to the printhead by a supply of ink that is either carried by the carriage or mounted to the printing system such that the supply of ink does not move with the carriage. For the case where the ink supply is not carried with the carriage, the ink supply can be in fluid communication with the printhead to replenish the printhead or the printhead can be intermittently connected with the ink supply by positioning the printhead proximate to a filling station to which the ink supply is connected whereupon the printhead is replenished with ink from the refilling station.
For the case where the ink supply is carried with the carriage, the ink supply may be integral with the printhead whereupon the entire printhead and ink supply is replaced when ink is exhausted. Alternatively, the ink supply can be carried with the carriage and be separately replaceable from the printhead.
For convenience, the concepts of the invention are discussed in the context of thermal inkjet printheads. A thermal inkjet printhead die includes an array of firing chambers having orifices (also called nozzles) which face the print media. The ink is applied to individually addressable ink energizing elements (such as firing resistors) within the firing chambers. Energy provided by the firing resistors heats the ink within the firing chambers causing the ink to bubble. This in turn causes the ink to be expelled out of the orifice of the firing chamber toward the print media. As the ink is expelled, the bubble collapses and more ink is drawn into the firing chambers, allowing for repetition of the ink expulsion process.
Inkjet printhead dies are in part manufactured using processes that employ photolithographic techniques similar to those used in semiconductor manufacturing. The components are constructed on a flat substrate layer of silicon by selectively adding layers of various materials and subtracting portions of the substrate layer and added layers using these photolithographic techniques. Some existing inkjet printhead dies are defined by a silicon substrate layer having firing resistors within a stack of thin film layers, a barrier layer and an orifice layer or orifice plate. Material removed from the barrier layer defines the firing chambers, while openings within the orifice layer or plate define the nozzles for the firing chambers.
In an inkjet printhead die, ink is delivered to the firing chambers and thereby the firing resistors by either a slotted ink delivery system or an edgefeed ink delivery system. In a slotted ink delivery system, the inkjet printhead die includes one or more slots that route ink from a backside of the printhead die to a front side where the firing resistors reside on at least one side of each of the slots. Typically, a single color printhead die includes a single ink delivery slot with one column of firing resistors on each side of the slot. However, a single color printhead die may include multiple slots to improve print quality and/or speed. A multicolor printhead die typically includes an ink delivery slot for each color. Generally, the printhead die is mounted to a printhead cartridge body using a structural adhesive. In multicolor print cartridges having a printhead die with multiple slots, this structural adhesive is deposited in a loop around each individual slot to separate out the individual ink colors.
Although this slotted ink delivery system for inkjet printhead dies adequately delivers ink the firing resistors, there are some disadvantages to this system of ink routing. The primary disadvantages are strength, size and waste. With regard to strength, in a printhead die, the ink delivery slot(s) structurally weaken the printhead die. As such, the greater the number of slots the weaker the die. With regard to size, the ink delivery slots can only be put so close together before manufacturability issues arise that causes manufacture of the printhead die to be accomplished in less than an optimal cost efficient manner. As such, the spacing of the ink delivery slots limits how small the printhead die can be. With regard to waste, approximately 300 μm of printhead die material (i.e. silicon) is lost by creating a slot. As such, the greater the number of slots, the greater the waste.
In an edgefeed ink delivery system, ink is routed from a backside of the printhead die, then around the edges of the die to a front side of the die where the firing resistors reside. Typically in an edgefeed ink delivery system, only the two long edges of the printhead die are used for ink feed, while the two short edges of the die are used for electrical connections. As such, the typical edgefeed printhead die includes only a single column of firing resistors adjacent each long edge. Since there are only two edges for ink flow, an edgefeed printhead die is limited to a maximum of two color inkjet printing, while in practice, the use of an edgefeed printhead die is almost exclusively used for single color printing. Generally, the orifice plate of the printhead die is oversized to permit mounting of the printhead die to a printhead cartridge body using a structural adhesive.
The edgefeed ink delivery system for inkjet printhead dies adequately delivers ink to the firing resistors. Moreover, edgefeed printhead dies have a large strength and utility advantage over slotted printhead dies because unlike slotted dies there are no ink delivery slots in an edgefeed die to weaken the die or cause waste. In addition, edgefeed printhead dies have a size advantage over slotted dies because the absence of ink delivery slots allows the edgefeed die to be made smaller. However, there is a disadvantage to the edgefeed die when compared to the slotted die, since the edgefeed die is limited to a maximum of two color printing while that slotted die can print as many colors as there are slots.
Typically to obtain print quality and speed, it is to necessary to maximize the density of the firing chambers (i.e. firing resistors) and/or increase the number of firing chambers. Maximizing the density of the firing chambers and/or increasing the number of firing chambers typically necessitates an increase in the size of the printhead die and/or a miniaturization of printhead die components. As discussed above, when the density is sufficiently high, conventional manufacturing by assembling separately produced components becomes more difficult and costly. In addition, the substrate that supports firing resistors, the barrier that isolates individual resistors, and the orifice plate that provides a nozzle above each resistor are all subject to small dimensional variations that can accumulate to limit miniaturization. Further, the assembly of such components for conventional printheads requires precision that limits manufacturing efficiency.
As such, there is a desire for a multicolor printhead die that is economical to manufacture, and relatively simple to incorporate into inkjet printhead cartridges usable in thermal inkjet printing systems.